This invention relates to hydroxyproline derivatives or their salts, to a therapeutic agent containing hydroxyproline derivatives or their salts for damaged organs and tissues, and to a method of treatment for damaged organs and tissues by administration of hydroxyproline derivatives or their salts.
It is well known that human placenta and its hydrolysate contain various biologically active substances. For instance, xe2x80x9ctissue therapiesxe2x80x9d with the hydrolysate of human placenta prepared by Filatov""s method have been used to treat chronic diseases such as asthma, rheumatism, hepatitis and anti-aging for its proliferative effect on elastic fibroblasts of blood vessels and myofibroblasts.
While human placenta and its hydrolysate are inferred to contain various biologically active substances as mentioned above, their primary effective substances are not yet known. Consequently, in the course of separating, purifying, and identifying the biologically active substances in the hydrolysate of human placenta, the inventors found hydroxyproline derivatives having cell-proliferative and cell-protective activities.
Based on these findings, the purposes of this invention are to provide novel hydroxyproline derivatives which stimulate the proliferation of cells, and to provide a therapeutic agent for damaged organs and tissues, which contain such hydroxyproline derivatives.
The compounds of this invention are hydroxyproline derivatives represented by the following general formulas (1) and (2) or their salts. 
(wherein R is hydrogen or alkyl group which may be substituted with hydroxy group, amino group, carboxy group, aminocarbonyl group, guanidino group, heterocyclic group, mercapto group, alkylthio group or phenyl group optionally substituted with hydroxy group)
In this invention, the therapeutic agent for damaged organs and tissues contains a hydroxyproline derivative represented by the following general formula (1), (2) or (3) or their salts, as an effective ingredient. 
(wherein R is the same as defined above)
The present invention also relates to the method of treatment for damaged organs and tissues comprising administration of an effective amount of hydroxyproline derivative represented by the above-mentioned formula (1), (2) or (3) or their salts, and a use of hydroxyproline derivative represented by the above-mentioned formula (1), (2) or (3) or their salts for manufacturing the therapeutic agent for damaged organs and tissues.
Further, as for the hydroxyproline derivatives represented by the general formulas (1), (2) and (3), the compounds in which R is hydroxymethyl are speculated to be the most useful.